1. Field of the Invention
The present invention relates to a composition based on calcium chloride hexahydrate for storing heat using a phase change, the efficiency range of which is below 23.degree. C. and which is suitable, consequently, particularly for recovering heat energy in dwellings and in covered cultivation installations such as greenhouses, and the process for the preparation of such a composition.
2. Background of the Art
In view particularly of its advantageous price and its high capacity for storing heat using a phase change, calcium chloride hexahydrate has already frequently been proposed as a basic component of heat storage compositions. However, since the melting point of calcium chloride hexahydrate is in the region of 29.degree. C., the compositions proposed hitherto are found not to be ideal for heat conditioning of dwellings and covered cultivation installations in which it is generally desired to maintain a temperature of 17.degree. to 23.degree. C. and, preferably, from 19.degree. to 22.degree. C.
To lower the melting point of the heat storage compositions based on calcium chloride hexahydrate, it has already been proposed by K. K. Meissingset and F. Grondvold, in the course of conferences held at Birmingham on 9 and 10 Sept. 1982 in connection with the storage of solar energy, to incorporate potassium chloride and/or ammonium chloride in these compositions. However, according to the tests described by these investigators, it appears that these additives do not make it possible to lower the melting point of the compositions beyond 23.degree. C. and thus make them perfectly efficient for use in dwellings and in greenhouses for cultivation.
It is possible to lower the melting point of a composition by adding a slight excess of water to it. This method, however, has the disadvantage of reducing the heat storage capacity and of considerably widening the temperature interval separating the beginning and the end of melting. This widening of the melting range further decreases the useful storage capacity, because the permissible temperature variations, particularly in the case of agricultural greenhouses, are only of a few degrees.